One who has a brother of any kind binds his brother's wife for yibum, and is [considered] his brother in all respects; except for someone who has [a brother] from a slave-woman or a non-Jewess.  One who has a son of any kind releases his father's wife from yibum, is liable for striking or cursing him, and is considered his son in every respect; except for someone who has [a son] from a slave-woman or a non-Jewess.

One who betrothed one of two sisters, but does not know which of them he betrothed, [must] divorce each of them. [If] he died and left one brother, he performs chalitzah with both. [If] he left two [brothers], one performs chalitzah and the other [may then] perform yibum. [However, if] they went ahead and married [them], we do not force them to divorce.